Screw Compressor System for a Utility Vehicle

ABSTRACT

A screw compressor system for a utility vehicle has at least one screw compressor, at least one screw compressor drive, at least one temperature probe and at least one control and regulation unit. The control and/or regulation unit is connected to the screw compressor drive and to the temperature probe and is designed and configured such that it controls, in accordance with a temperature threshold signal obtained from the temperature probe, the screw compressor drive with respect to a rotational speed.

BACKGROUND AND SUMMARY OF THE INVENTION

The present invention relates to a screw compressor system for a utilityvehicle, having at least one screw compressor with at least oneopen-loop and/or closed-loop control unit for the open-loop and/orclosed-loop drive control of the screw compressor.

Screw compressors for utility vehicles are already known from the priorart. Such screw compressors are used to provide the compressed airrequired for the brake system of the utility vehicle, for example.

In this context, in particular oil-filled compressors, in particularalso screw compressors, are known, in the case of which it is necessaryto regulate the oil temperature. This is generally realized by virtue ofan external oil cooler being provided which is connected to theoil-filled compressor and to the oil circuit via a thermostat valve.Here, the oil cooler is a heat exchanger which has two mutually separatecircuits, wherein the first circuit is provided for the hot liquid, thatis to say the compressor oil, and the second circuit is provided for thecooling liquid. As cooling liquid, use may for example be made of air,water mixtures with an antifreeze, or another oil.

This oil cooler must then be connected to the compressor oil circuit bymeans of pipes or hoses, and the oil circuit must be safeguarded againstleakage.

This external volume must furthermore be filled with oil, such that thetotal quantity of oil is also increased. The system inertia is thusincreased. Furthermore, the oil cooler must be mechanically accommodatedand fastened, either by means of brackets situated in the surroundingsor by means of a separate bracket, which necessitates additionalfastening means and also structural space.

U.S. Pat. No. 4,780,061 has already disclosed a screw compressor with anintegrated oil cooling arrangement.

Furthermore, DE 37 17 493 A1 discloses a screw compressor installationwhich is arranged in a compact housing and which has an oil cooler onthe electric motor of the screw compressor.

A generic screw compressor is already known for example from DE 10 2004060 417 B4.

It is the object of the present invention to advantageously furtherdevelop a screw compressor system of the type mentioned in theintroduction, in particular such that the open-loop and/or closed-loopdrive control of the screw compressor can be made simpler and reliable.

This object is achieved according to the invention by a screw compressorsystem for a utility vehicle having at least one screw compressor, atleast one screw compressor drive, at least one temperature sensor and atleast one open-loop and/or closed-loop control unit. The open-loopand/or closed-loop control unit is connected to the screw compressordrive and to the temperature sensor, wherein the open-loop and/orclosed-loop control unit is configured so as to control the screwcompressor drive with regard to its rotational speed in a mannerdependent on a temperature threshold value signal received from thetemperature sensor.

The invention is based on the underlying concept that temperaturemanagement of the screw compressor system can be achieved by virtue ofthe screw compressor drive being correspondingly controlled in a mannerdependent on the temperature in the screw compressor. The rotationalspeed of the screw compressor drive also significantly influences thetemperature of the screw compressor. If a certain temperature isreached, then it is possible, through adaptation of the rotational speedof the screw compressor drive, for the temperature to be correspondinglyincreased or else lowered. In particular, provision may be made for thescrew compressor system to be of relatively large design, such that,owing to the oil quantity present in the screw compressor, a certaininertia exists such that temperature changes occur. It is alsoconceivable for the screw compressor system to be one which is designednormally for part-load operation or operation at low load, and whichdoes not need to be constantly operated at full load.

For example, provision may be made for the open-loop and/or closed-loopcontrol unit to be a constituent part of the screw compressor system. Inthis way, a compact construction is formed, and it is not necessary toresort to external components.

It is however basically also conceivable for the open-loop and/orclosed-loop control unit to be a constituent part of an air treatmentsystem of the utility vehicle. Here, a corresponding controller isalready provided, which can easily be jointly utilized.

It is also conceivable for the open-loop and/or closed-loop control unitto be a constituent part of an engine or vehicle controller of theutility vehicle. Here, too, it would be possible to resort to anexisting component of the utility vehicle.

It is however basically also conceivable for the open-loop and/orclosed-loop control unit to be in the form of a separate open-loopand/or closed-loop control unit. This permits, for example, easyinstallation and also an easy exchange or easy upgrades.

Furthermore, provision may be made for the open-loop and/or closed-loopcontrol unit to be designed and configured to deactivate the screwcompressor drive upon receipt of a temperature threshold value signalthat signals an overshooting of a predetermined temperature thresholdvalue in the screw compressor. In this way, a temperature reduction inthe screw compressor can be achieved in a very short time in a simpleand effective manner. In the absence of operation of the screwcompressor, which is achieved by deactivation of the screw compressordrive, no further generation of heat occurs in the screw compressor,such that the latter can cool down.

It is furthermore conceivable for the open-loop and closed-loop controlunit to be designed and configured to permit an activation of the screwcompressor drive only if said open-loop and closed-loop control unitreceives a temperature threshold value signal that signals anundershooting of a predetermined temperature threshold value in thescrew compressor. The temperature threshold value signal that signals anundershooting of a predetermined temperature threshold value in thescrew compressor may basically differ from a temperature threshold valuesignal which is received by the open-loop and/or closed-loop controlunit by means of which a deactivation of the screw compressor drive istriggered. These temperature threshold value signals may however also beidentical. By preventing a start or restart of the screw compressor inthe presence of an excessively high temperature, simple but at the sametime reliable open-loop and/or closed-loop control of the temperature inthe screw compressor system or in the screw compressor is likewise madepossible.

Provision may be made for the screw compressor system to have nothermostat valve. It is basically conceivable that, on the basis of theconfiguration of the open-loop and/or closed-loop control unit, thetemperature management of the screw compressor can be implemented withsuch effectiveness that there is no need whatsoever for a heat-dependentactivation of an oil cooling circuit, which commonly has a thermostatvalve. This component of the screw compressor system can thus beomitted.

Provision may basically also be made for the screw compressor system tohave no heat exchanger for oil cooling. Through the omission of thisrelatively expensive component, the construction of the screw compressorsystem can be simplified overall.

Further details and advantages of the invention will now be discussed inmore detail on the basis of an exemplary embodiment illustrated in thedrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a schematic sectional drawing through a screw compressoraccording to the invention; and

FIG. 2 shows a schematic drawing of the screw compressor systemaccording to the present invention.

DETAILED DESCRIPTION OF THE DRAWINGS

FIG. 1 shows, in a schematic sectional illustration, a screw compressor10 in the context of an exemplary embodiment of the present invention.

The screw compressor 10 has a fastening flange 12 for the mechanicalfastening of the screw compressor 10 to an electric motor (not shown inany more detail here).

What is shown, however, is the input shaft 14, by which the torque fromthe electric motor is transmitted to one of the two screws 16 and 18,specifically the screw 16.

The screw 18 meshes with the screw 16 and is driven by means of thelatter.

The screw compressor 10 has a housing 20 in which the main components ofthe screw compressor 10 are accommodated.

The housing 20 is filled with oil 22.

At the air inlet side, an inlet connector 24 is provided on the housing20 of the screw compressor 10. The inlet connector 24 is in this casedesigned such that an air filter 26 is arranged at said inlet connector.Furthermore, an air inlet 28 is provided radially on the air inletconnector 24.

In the region between the inlet connector 24 and the point at which theinlet connector 24 joins to the housing 20, there is provided aspring-loaded valve insert 30, which is designed here as an axial seal.

This valve insert 30 serves as a check valve.

Downstream of the valve insert 30, there is provided an air feed channel32 which feeds the air to the two screws 16, 18.

At the outlet side of the two screws 16, 18, there is provided an airoutlet pipe 34 with a riser line 36.

In the region of the end of the riser line 36, there is provided atemperature sensor 38 by means of which the oil temperature can bemonitored.

Also provided in the air outlet region is a holder 40 for an airdeoiling element 42.

In the assembled state, the holder 40 for the air deoiling element hasthe air deoiling element 42 in the region facing toward the base (asalso shown in FIG. 1).

Also provided, in the interior of the air deoiling element 42, is acorresponding filter screen or known filter and oil separation devices44, which will not be specified in any more detail.

In the central upper region in relation to the assembled andoperationally ready state (that is to say as shown in FIG. 1), theholder for the air deoiling element 42 has an air outlet opening 46which leads to a check valve 48 and a minimum pressure valve 50. Thecheck valve 48 and the minimum pressure valve 50 may also be formed inone common combined valve.

The air outlet 51 is provided downstream of the check valve 48.

The air outlet 51 is generally connected to correspondingly knowncompressed-air consumers.

In order for the oil 22 that is situated and separated off in the airdeoiling element 42 to be returned into the housing 20, a riser line 52is provided which has a filter and check valve 54 at the outlet of theholder 40 for the air deoiling element 42 at the transition into thehousing 20.

A nozzle 56 is provided, downstream of the filter and check valve 54, ina housing bore. The oil return line 58 leads back into approximately thecentral region of the screw 16 or of the screw 18 in order to feed oil22 thereto again.

An oil drain screw 59 is provided in the base region, in the assembledstate, of the housing 20. By means of the oil drain screw 59, acorresponding oil outflow opening can be opened, via which the oil 22can be drained.

Also provided in the lower region of the housing 20 is the attachmentpiece 60 to which the oil filter 62 is fastened. Via an oil filter inletchannel 64, which is arranged in the housing 20, the oil 22 is conductedfirstly to a thermostat valve 66.

Instead of the thermostat valve 66, it is possible for an open-loopand/or closed-loop control device to be provided by means of which theoil temperature of the oil 22 situated in the housing 20 can bemonitored and set to a setpoint value.

Downstream of the thermostat valve 66, there is then the oil inlet ofthe oil filter 62, which, via a central return line 68, conducts the oil22 back to the screw 18 or to the screw 16 again, or else to theoil-lubricated bearing 70 of the shaft 14. Also provided in the regionof the bearing 70 is a nozzle 72, which is provided in the housing 20 inconjunction with the return line 68.

The cooler 74 is connected to the attachment piece 60, as will bediscussed in more detail below in FIGS. 2 to 4.

In the upper region of the housing 20 (in relation to the assembledstate), there is situated a safety valve 76, by means of which anexcessively high pressure in the housing 20 can be dissipated.

Upstream of the minimum pressure valve 50, there is situated a bypassline 78, which leads to a relief valve 80. Via said relief valve 80,which is activated by means of a connection to the air feed 32, air canbe returned into the region of the air inlet 28. In this region, theremay be provided a ventilation valve (not shown in any more detail) andalso a nozzle (diameter constriction of the feeding line).

Furthermore, approximately at the level of the line 34, an oil levelsensor 82 may be provided in the outer wall of the housing 20. Said oillevel sensor 82 may for example be an optical sensor, and may bedesigned and configured such that, on the basis of the sensor signal, itcan be identified whether the oil level during operation is above theoil level sensor 82 or whether the oil level sensor 82 is exposed, andthus the oil level has correspondingly fallen.

In conjunction with this monitoring, it is also possible for an alarmunit to be provided which outputs or transmits a corresponding errormessage or warning message to the user of the system.

The function of the screw compressor 10 shown in FIG. 1 is as follows.

Air is fed via the air inlet 28 and passes via the check valve 30 to thescrews 16, 18, where the air is compressed. The compressed air-oilmixture, which, having been compressed by a factor of between 5 and 16downstream of the screws 16 and 18, rises through the outlet line 34 viathe riser pipe 36, is blown directly onto the temperature sensor 38.

The air, which still partially carries oil particles, is then conductedvia the holder 40 into the air deoiling element 42 and, if thecorresponding minimum pressure is attained, passes into the air outletline 51.

The oil 22 situated in the housing 20 is kept at operating temperaturevia the oil filter 62 and possibly via the heat exchanger 74.

If no cooling is necessary, the heat exchanger 74 is not used and isalso not activated.

The corresponding activation is performed by means of the thermostatvalve 66. After purification in the oil filter 62, oil is fed via theline 68 to the screw 18 or to the screw 16, or else to the bearing 70.The screw 16 or the screw 18 is supplied with oil 22 via the return line52, 58, and the purification of the oil 22 takes place here in the airdeoiling element 42.

By means of the electric motor (not shown in any more detail), whichtransmits its torque via the shaft 14 to the screw 16, which in turnmeshes with the screw 18, the screws 16 and 18 of the screw compressor10 are driven.

By means of the relief valve 80 (not shown in any more detail), it isensured that the high pressure that prevails for example at the outletside of the screws 16, 18 in the operational state cannot be enclosed inthe region of the feed line 32, and that, instead, in particular duringthe start-up of the compressor, there is always a low inlet pressure, inparticular atmospheric pressure, prevailing in the region of the feedline 32. Otherwise, upon a start-up of the compressor, a very highpressure would initially be generated at the outlet side of the screws16 and 18, which would overload the drive motor.

FIG. 2 shows, in a schematic illustration, a screw compressor system 100according to the invention, having the screw compressor 10 shown in FIG.1.

The screw compressor system 100 furthermore has an open-loop and/orclosed-loop control unit 110, which is connected to the temperaturesensor 38 and to the drive of the screws 16 and 18 of the screwcompressor 10 (the electric motor, which is not shown in any moredetail, and which transmits its torque to the input shaft 14).

Here, the open-loop and closed-loop control unit 110 is formed as aconstituent part of the screw compressor 10.

Provision may however basically be made for the open-loop andclosed-loop control unit 110 to be formed as a constituent part of anair treatment system (not shown in any more detail) of the utilityvehicle, as a constituent part of an engine or vehicle controller of theutility vehicle, or as a separate open-loop and closed-loop control unit110.

The open-loop and/or closed-loop control unit 110 is designed andconfigured so as to control the screw compressor drive with regard toits rotational speed in a manner dependent on a temperature thresholdvalue signal received from the temperature sensor 38.

Here, provision is made in particular for the open-loop and closed-loopcontrol unit 110 to deactivate the screw compressor drive upon receiptof a temperature threshold value signal that signals an overshooting ofthe predetermined temperature threshold value in the screw compressor10.

A start-up of the screw compressor is possible again only when atemperature threshold value signal that signals an undershooting of apredetermined temperature threshold value in the screw compressor 10 istransmitted from the temperature sensor 38 to the open-loop andclosed-loop control unit 110.

The temperature threshold value for the activation and deactivation ofthe screw compressor 10 is in this case preferably selected to beidentical in order to permit simple implementation.

Provision may however basically also be made for different thresholdvalues to be provided for this purpose.

The temperature threshold value may for example be selected to beapproximately 10 to 30% above the normal working temperature.

By means of the embodiment shown in FIG. 2, it can be achieved that thescrew compressor system 100, or the screw compressor 10, no longer needsto have a thermostat valve 66, and also no longer needs to have a heatexchanger 74.

LIST OF REFERENCE DESIGNATIONS

-   10 Screw compressor-   12 Fastening flange-   14 Input shaft-   16 Screws-   18 Screws-   20 Housing-   22 Oil-   24 Inlet connector-   26 Air filter-   28 Air inlet-   30 Valve insert-   32 Air feed channel-   34 Air outlet pipe-   36 Riser line-   38 Temperature sensor-   40 Holder for an air deoiling element-   42 Air deoiling element-   44 Filter screen or known filter or oil separation devices-   46 Air outlet opening-   48 Check valve-   50 Minimum pressure valve-   51 Air outlet-   52 Riser line-   54 Filter and check valve-   56 Nozzle-   58 Oil return line-   59 Oil drain screw-   60 Attachment piece-   60 a Outer ring-   60 b Inner ring-   62 Oil filter-   64 Oil filter inlet channel-   66 Thermostat valve-   68 Return line-   70 Bearing-   72 Nozzle-   74 Cooler, heat exchanger-   76 Safety valve-   78 Bypass line-   80 Relief valve-   82 Oil level sensor-   100 Screw compressor system-   110 Open-loop and/or closed-loop control unit

1-9. (canceled)
 10. A screw compressor system for a utility vehicle,comprising: at least one screw compressor; at least one screw compressordrive; at least one temperature sensor; and at least one open-loopand/or closed-loop control unit, wherein the open-loop and/orclosed-loop control unit is connected to the screw compressor drive andto the temperature sensor, the open-loop and/or closed-loop control unitis configured so as to control the screw compressor drive with regard toa rotational speed thereof in a manner dependent on a temperaturethreshold value signal received from the temperature sensor.
 11. Thescrew compressor system as claimed in claim 10, wherein the open-loopand/or closed-loop control unit is a constituent part of the screwcompressor.
 12. The screw compressor system as claimed in claim 10,wherein the open-loop and/or closed-loop control unit is a constituentpart of an air treatment system of the utility vehicle.
 13. The screwcompressor system as claimed in claim 10, wherein the open-loop and/orclosed-loop control unit is a constituent part of an engine or vehiclecontroller of the utility vehicle.
 14. The screw compressor system asclaimed in claim 10, wherein the open-loop and/or closed-loop controlunit is a separate open-loop and/or closed-loop control unit.
 15. Thescrew compressor system as claimed in claim 10, wherein the open-loopand/or closed-loop control unit is configured to deactivate the screwcompressor drive upon receipt of a temperature threshold value signalthat signals an overshooting of a predetermined temperature thresholdvalue in the screw compressor.
 16. The screw compressor system asclaimed in claim 10, wherein the open-loop and/or closed-loop controlunit is configured to permit an activation of the screw compressor driveonly if said open-loop and/or closed-loop control unit receives atemperature threshold value signal that signals an undershooting of apredetermined temperature threshold value in the screw compressor. 17.The screw compressor system as claimed in claim 10, wherein the screwcompressor system has no thermostat valve.
 18. The screw compressorsystem as claimed in claim 17, wherein the screw compressor system hasno heat exchanger for oil cooling.
 19. The screw compressor system asclaimed in claim 10, wherein the screw compressor system has no heatexchanger for oil cooling.